The routine eliminates all pairs of observations xi,yi which contain a missing value for either x or y, and then calculates the regression coefficient, b, the regression constant, a, and various other statistical quantities, by minimizing the sum of the ei2 over those cases remaining in the calculations.

The input data consists of the n pairs of observations x1,y1,x2,y2,…,xn,yn on the independent variable x and the dependent variable y.

In addition two values, xm and ym, are given which are considered to represent missing observations for x and y respectively. (See Section 7).

Let wi=0 if the ith observation of either x or y is missing, i.e., if xi=xm and/or yi=ym; and wi=1 otherwise, for i=1,2,…,n.

The quantities calculated are:

(a)

Means:

x-=∑i=1nwixi∑i=1nwi; y-=∑i=1nwiyi∑i=1nwi.

(b)

Standard deviations:

sx=∑i=1nwixi-x-2∑i=1nwi-1; sy=∑i=1nwiyi-y-2∑i=1nwi-1.

(c)

Pearson product-moment correlation coefficient:

r=∑i=1nwixi-x-yi-y-∑i=1nwixi-x-2∑i=1nwiyi-y-2.

(d)

The regression coefficient, b, and the regression constant,
a:

b=∑i=1nwixi-x-yi-y-∑i=1nwixi-x-2, a=y--bx-.

(e)

The sum of squares attributable to the regression, SSR, the sum of squares of deviations about the regression, SSD, and the total sum of squares, SST:

SST=∑i=1nwiyi-y-2; SSD=∑i=1nwiyi-a-bxi2; SSR=SST-SSD.

(f)

The degrees of freedom attributable to the regression, DFR, the degrees of freedom of deviations about the regression, DFD, and the total degrees of freedom, DFT:

DFT=∑i=1nwi-1; DFD=∑i=1nwi-2; DFR=1.

(g)

The mean square attributable to the regression, MSR, and the mean square of deviations about the regression, MSD:

MSR=SSR/DFR; MSD=SSD/DFD.

(h)

The F value for the analysis of variance:

F=MSR/MSD.

(i)

The standard error of the regression coefficient, seb, and the standard error of the regression constant, sea:

seb=MSD∑i=1nwixi-x-2; sea=MSD1∑i=1nwi+x-2∑i=1nwixi-x-2.

(j)

The t value for the regression coefficient, tb, and the t value for the regression constant, ta:

On entry: the value xm which is to be taken as the missing value for the variable x. See Section 7.

5: YMISS – REAL (KIND=nag_wp)Input

On entry: the value ym which is to be taken as the missing value for the variable y. See Section 7.

6: RESULT(21) – REAL (KIND=nag_wp) arrayOutput

On exit: the following information:

RESULT1

x-, the mean value of the independent variable, x;

RESULT2

y-, the mean value of the dependent variable, y;

RESULT3

sx, the standard deviation of the independent variable, x;

RESULT4

sy, the standard deviation of the dependent variable, y;

RESULT5

r, the Pearson product-moment correlation between the independent variable x and the dependent variable y

RESULT6

b, the regression coefficient;

RESULT7

a, the regression constant;

RESULT8

seb, the standard error of the regression coefficient;

RESULT9

sea, the standard error of the regression constant;

RESULT10

tb, the t value for the regression coefficient;

RESULT11

ta, the t value for the regression constant;

RESULT12

SSR, the sum of squares attributable to the regression;

RESULT13

DFR, the degrees of freedom attributable to the regression;

RESULT14

MSR, the mean square attributable to the regression;

RESULT15

F, the F value for the analysis of variance;

RESULT16

SSD, the sum of squares of deviations about the regression;

RESULT17

DFD, the degrees of freedom of deviations about the regression;

RESULT18

MSD, the mean square of deviations about the regression;

RESULT19

SST, the total sum of squares;

RESULT20

DFT, the total degrees of freedom;

RESULT21

nc, the number of observations used in the calculations.

7: IFAIL – INTEGERInput/Output

On entry: IFAIL must be set to 0, -1​ or ​1. If you are unfamiliar with this parameter you should refer to Section 3.3 in the Essential Introduction for details.

For environments where it might be inappropriate to halt program execution when an error is detected, the value -1​ or ​1 is recommended. If the output of error messages is undesirable, then the value 1 is recommended. Otherwise, if you are not familiar with this parameter, the recommended value is 0. When the value -1​ or ​1 is used it is essential to test the value of IFAIL on exit.

On exit: IFAIL=0 unless the routine detects an error or a warning has been flagged (see Section 6).

6 Error Indicators and Warnings

If on entry IFAIL=0 or -1, explanatory error messages are output on the current error message unit (as defined by X04AAF).

Errors or warnings detected by the routine:

IFAIL=1

On entry,

N≤2.

IFAIL=2

After observations with missing values were omitted, two or fewer cases remained.

IFAIL=3

After observations with missing values were omitted, all remaining values of at least one of the variables x and y were identical.

7 Accuracy

G02CCF does not use additional precision arithmetic for the accumulation of scalar products, so there may be a loss of significant figures for large n.

You are warned of the need to exercise extreme care in your selection of missing values. G02CCF treats all values in the inclusive range 1±0.1X02BEF-2×xmj, where xmj is the missing value for variable j specified in XMISS.

You must therefore ensure that the missing value chosen for each variable is sufficiently different from all valid values for that variable so that none of the valid values fall within the range indicated above.

If, in calculating
F or ta
(see Section 3), the numbers involved are such that the result would be outside the range of numbers which can be stored by the machine, then the answer is set to the largest quantity which can be stored as a real variable, by means of a call to X02ALF.

8 Further Comments

The time taken by G02CCF depends on n and the number of missing observations.

The routine uses a two-pass algorithm.

9 Example

This example reads in eight observations on each of two variables, and then performs a simple linear regression with the first variable as the independent variable, and the second variable as the dependent variable, omitting cases involving missing values (0.0 for the first variable, 99.0 for the second). Finally the results are printed.